This invention relates to an electrically heated recording indicator for use in a recording instrument utilizing a thermosensitive recording medium.
In a recording indicator the heated writing tube is designed to be placed during the writing operation in direct contact with the surface of the thermosensitive recording medium, e.g. recording paper. The writing tube is normally composed of either metal or a ceramic. A disadvantage of metallic writing tubes is that they are generally subject to a relatively high rate of wear. In addition, the time required to heat a metallic writing tube is relatively long. When a metallic writing tube is used, the quality of the writing, particularly in the case of high-speed recording, is often of poor quality because the heat from an electrically heated coil located in the writing tube is transmitted via an insulating pipe of poor heat conductivity or via air to the writing tube. Due to its relatively good thermal conductivity, a metallic writing tube dissipates heat from its source at a high rate so that insufficient heat is transferred to the thermosensitive recording medium during writing.
In the case of a ceramic writing tube, heat is transmitted from an electrical heating source via air to the writing tube which is in direct contact with the thermosensitive recording medium. An electrically conductive bear extending along the ceramic tube is fixed to one end of the ceramic tube, the other end being connected electrically with one end of the heating coil. A disadvantage of this arrangement is the high specific gravity and the high air resistance, both of which tend to retard fast movement of the ceramic writing tube. Furthermore, the ceramic writing tube is subject to mechanical damage.
The weight of a recording indicator should be as low as possible; and its mass, inertia and air resistance should also be low to assure accurate recording. Moreover, the intrinsic resonance of the recording indicator should be in a frequency range above the highest frequency to be recorded so as to avoid recording errors.
An object of the present invention is to provide a recording indicator of the type described which avoids the abovementioned disadvantages and provides excellent writing quality, durability and accuracy.